A compression ignition internal combustion engine (ICE) for a motor vehicle generally includes an engine block which defines at least one cylinder accommodating a reciprocating piston coupled to rotate a crankshaft. The cylinder is closed by a cylinder head that cooperates with the reciprocating piston to define a combustion chamber. A fuel and air mixture is cyclically disposed in the combustion chamber and ignited, thereby generating hot expanding exhaust gasses that cause the reciprocating movements of the piston. The fuel is injected into each cylinder by a respective fuel injector. The fuel is provided at high pressure to each fuel injector from a fuel rail in fluid communication with a high pressure fuel pump that increase the pressure of the fuel received from a fuel source.
After the expansion, the exhaust gases exit the combustion chamber and are directed into an exhaust system, which generally includes an exhaust pipe having one or more aftertreatment devices configured to fitter and/or change the composition of the exhaust gases, such as for example a Diesel Oxidation Catalyst (DOC), a Diesel Particulate Filter (DPF), a Lean NOx Trap (LNT), and/or a Selective Catalytic Reduction (SCR) system or a SCRF (SCR on Filter).
In order to guarantee and/or restore the efficiency of some of these aftertreatment devices, it may be necessary to perform suitable regeneration procedures. For example, the particulate matter that progressively accumulates inside a particulate filter (DPF) must be periodically removed to prevent an excessive pressure drop across the filter. This process, which is conventionally known as DPF regeneration, is achieved by increasing the temperature of the exhaust gases entering the DPF (typically up to 630° C.), which in turn heat the filter up to a temperature at which the accumulated particulate burns off.
A known strategy to increase the exhaust gas temperature provides for the exhaust gases to be mixed with a certain amount of unburned fuel (HC) that oxidizes in the oxidation catalyst, thereby heating the exhaust gases that subsequently pass through the DPR.
The unburned fuel may come from the engine cylinder thanks to the so called after or post-injections or, in some automotive systems, may be supplied by means of a dedicated fuel injector.
In order to start a DPF regeneration when the DPF is deemed bill of particulates, an Electronic Control Unit (ECU) of the vehicle continuously estimates the amount of emitted particulates since the last DPF regeneration on the basis of engine operating parameters. DPF regeneration is initiated as soon as those estimates by the ECU reach a predefined physical threshold.
DPF regeneration is preferably initiated during conditions requiring low EGR rates (e.g. less than 50%). For example, DPF regeneration is preferably initiated during cruising at highway speeds. DPF regeneration, however, can be initiated at less than optimum conditions if required.
Another aftertreatment device is the Lean NOx Trap (LNT), namely a device the traps nitrogen oxides (NOx) contained in the exhaust gas and is located in the exhaust line upstream of a Diesel Particulate Filter (DPF) In some embodiments, the LNT and the DPF are closely coupled in a single component.
The LNT is a catalytic device containing catalysts, such as Rhodium, Pt and Pd, and adsorbents, such as barium based elements, which provide active sites suitable for binding the nitrogen oxides (NOx) contained in the exhaust gas, in order to trap them within the device itself.
Also Lean NOx Traps (LNT) must be subjected to periodic regeneration processes or events, as soon as a physical threshold estimated by the ECU is reached, whereby such regeneration processes are generally provided to release and reduce the trapped nitrogen oxides (NOx) from the LNT. For this reason, Lean NOx Traps (LNT) are operated cyclically, for example by switching the engine from a lean burn operation to a rich operation, performing a regeneration event also referenced as DeNOx regeneration.
Also, in order to release accumulated sulphur from the LNT, DeSOx regeneration events are periodically performed by means of several rich combustion phases executed at high temperature, where gas temperature in the LNT may be around 650° C., each rich combustion phase being followed by a lean combustion phase, whereby this lean-to-rich-to-lean approach is also referred as wobbling approach. A DeSOx regeneration is generally performed at the same time during which a DPF regeneration is performed.
The LNT regenerations are obtained by operating the engine actuators, such as the injectors, the rail valve, the variable geometry turbine (VGT), the Exhaust Gas Recirculation system (EGD), the swirl valve, the throttle valve and the cooler bypass, all of which are moved to dedicated set points in order to achieve the desired combustion properties, using information coming mainly from temperature and lambda sensors positioned upstream and downstream of the LNT.
A problem with conventional systems is that a regeneration of an aftertreatment device, such as a DPF or a LNT, is generally started only on the basis of the physical needs of the aftertreatment device itself, as determined by a mathematical or statistical model of the physical conditions of the aftertreatment device with no regard to the mission profile of the vehicle or other variables. Consequently, a regeneration may, in many cases, be interrupted before it is completed or may be conducted at a low efficiency, for example in urban driving conditions, with consequently high oil dilution and high regeneration duration.